The Park Tool one is definitely worth spending £15 on. Makes your life easier when the tool fits perfectly each time and operates smoothly.
I've got a cheaper Icetoolz one as well and it really is a piece of crap in comparison.
Another vote for the Park extractor from me. Had mine about a decade and still going strong, though admittedly it sees less use than before as 2 of my bikes now have self-extracting bolts fitted.
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